The present invention concerns a capillary column which can be used in a liquid chromatograph, a gas chromatograph, an electrophoretic equipment, a solid state extraction apparatus and so forth.
In the conventional liquid chromatography, smaller column volume is favored for reducing the consumption of mobile phase. For the purpose of maintaining a high analytical performance, the column diameter instead of column length is reduced. A column with reduced diameter, called capillary column, is usually prepared by stuffing inorganic packing materials such as silica gels in a capillary by physical means.
The packing materials used in electrochromatography should carry electrostatic charge on their surfaces. Accordingly, inorganic porous materials which retain stable negative charges in a neutral pH condition, especially silica gels, are widely used.
The sol-gel method is one of liquid phase reaction paths to produce inorganic porous materials, especially silica gels. The sol-gel method denotes widespread processes in which polymerizable low molecular weight species are first generated, and through polymerization reactions, aggregated or polymerized materials are finally obtained. For example, the sol-gel method can be applied by hydrolyzing metal alkoxides, metal chlorides, metal salts or coordinated compounds which typically contain carboxyl or beta-diketone ligands.
Particle-packed capillary columns for electrochromatography have been prepared by physically packing inorganic particulate materials into a capillary. In order to avoid the change in the packing state of the particles due to their motion in the capillary, the both ends of a capillary are fitted with the parts called xe2x80x9cfritxe2x80x9d with relatively low porosity.
Particle-packed capillary columns are disadvantageous in the points that: (a) the packing procedure is complicated and time-consuming. (b) the reproducibility of the packing state, and correspondingly that of an excellent analytical performance, is poor. (c) Since the homogeneous packing of an entire capillary becomes increasingly difficult as the column length increases, an improvement of the analytical performance by increasing the total column length is not practical.
In addition, particle-packed capillary columns equipped with the frits at both ends frequently cause bubbling at the space between the frit and packed-beds, thus require additional pressurization for normal chromatographic operation.
In spite of the fact that the analytical performance of a capillary column is governed by its inner porous structure directly related to the packing state of the particles, no particle-packing method which produces the stable and reproducible packing state has been established.
Further, although smaller particle size is required for acclerated separation, the applied pressure becomes high for a capillary packed with smaller particles, which makes it difficult for practical uses.
The present inventors have found that: A capillary column which exhibits homogeneous and continuous double pore structure through the whole length of the capillary can be obtained by the processes of; 1) to form a three-dimensional co-continuous network consisting of an inorganic gel phase and a solvent phase both having average domain size of larger than 100 nm via a sol-gel process from a solution precursor containing a thermally decomposable component in a capillary with the inner diameter of less than 1 mm, 2) to modify the nanometer-range microstructures into that consisting of sharply distributed mesopores smaller than 50 nm in diameter by heating the wet gel to decompose said thermally decomposable component, 3) to dry and heat-treat the gel to obtain completely inorganic porous material. EP 0 710 219 discloses in detail procedures suitable for preparing porous silica materials with defined macro and meso pores. WO 98/29 350 discloses the use of thermolysable compounds to modify the pore structure of micropores. EP 98/08 295 is concerned with processes to make inorganic porous materials in a narrow bored column.
The present invention has been developed based on the above knowledge. The invention provides capillary columns with a well-defined and highly reproducible internal pore structure through the whole length of the capillary. Also the capillary consumes less mobile phase, requires lower column pressure, and provides an excellent analytical performance.